The present invention relates to switches for connecting an antenna to either a transmitter or a receiver. More particularly, it relates to a self-biased solid-state switch for coupling a radio frequency (RF) antenna with either a transmitter or a receiver in a communication system.
It has long been recognized that, in order to prevent damage to an RF receiver, the RF power from a transmitter should be prevented from reaching the receiver connected to the same antenna as the transmitter. Further, it is desirable that the receiver be decoupled from the antenna when an overload condition occurs, such as a power surge at the antenna.
Mechanical switches for performing these functions are either too slow or prone to failure. Electronic switches have been proposed, but their use has been limited by the amount of power they can switch.
Typically, electronic switches apply a reverse biasing voltage to a diode and thereby restrict the flow of the RF current from the transmitter to the receiver. To restrict the RF current flow, the reverse biasing voltage must at least be equal to the RF voltage. For low power transmitters, a typical low voltage power source such as a battery has been found to provide sufficient reverse biasing current. See, for example, U.S. Pat. No. 3,227,954 dated Jan. 4, 1966 to Fichter, Jr.
This arrangement, however, is not useful when the transmitter has more voltage than the battery. This is true, for example, in certain mobile communication systems where weight and space restrictions preclude the use of high voltage batteries. To provide the required voltage, it has been proposed that the magnitude of the RF signal energy be adapted to maintain the diode in a reverse biasing or nonconducting state. This approach, however, does not account for power losses in the circuit or for surges in power at the antenna. See, for example, U.S. Pat. No. 4,637,065 dated Jan. 13, 1987 to Ruppel.
To prevent power surges at the antenna from damaging the receiver, it has been proposed that the surge voltage be used to reverse bias the receiver diode, thereby decoupling the receiver from the antenna. The surge voltage is so used when it exceeds a predetermined standard. As with Ruppel, this approach does not account for circuit losses. See, for example, U.S. Pat. No. 4,525,863 dated June 25, 1985 to Stites.
Accordingly, it is an object of the present invention to provide an electronic switch that obviates the problems of the prior art and that is able to be used where the transmitter voltage far exceeds the switch's biasing voltage.
It is another object of the present invention to provide an electronic switch that combines in one circuit the ability to obtain a bias voltage directly from the RF power signal and to protect the receiver from possible overload.
It is yet another object of the present invention to provide an electronic switch that uses a voltage increaser to provide the bias voltage from the RF power signal.
It is a further object of the present invention to provide an electronic switch that uses a voltage doubler to protect the receiver circuit by doubling the input signal to reverse bias the receiver diode whenever a power detector circuit detects an overload condition.
These and many other objects and advantages will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.